When Kylie Minogue alights at the Cannes round table, the guests rise up and block her from view. Everyone has their hand outstretched, clamouring for an introduction. This journalist is from Portugal and that one's from Tasmania. "Wow!" exclaims Kylie as each country is namechecked. They'll eat her up, they love her so. Hello Kylie, I'm from London. "Wow!" says Kylie, beaming excitedly into my face as though I've told her I'm magic.

The singer is in Cannes to attend the grand unveiling of Holy Motors, a film that erupts in the main competition like some gaudy firework display, spooking the dignitaries and splitting the critics. Some say, "Wow!" And some say, "Wah!", though neither camp can pin it down. Leos Carax's picture is flamboyant and preposterous; completely joyous and wholly unclassifiable. Denis Lavant plays a chameleonic actor on assignment, ferried around Paris in a white limousine and changing en route from beggar-woman to satyr to assassin to victim. Minogue crops up late as a tragic, trenchcoated femme fatale, singing a torch song inside the derelict Samaritaine department store. At night, in the garage, the limousines start talking to each other.

Kylie shakes her head in wonderment. "I need to see it again in order to form an opinion of what it all means?" she says, her bright uplift turning statements into questions. "I'm still flabbergasted. I mean, it's overwhelmingly beautiful? And it's not depressing, even though there's a lot of darkness in there, too. It's got talking cars? It's hilarious."

She explains that she was introduced to Carax by a mutual friend, the French director Claire Denis. She first hit it off with Denis when they met at the hairdresser ("basically, life revolves around the hair salon"). Carax, for his part, had barely heard of her and this was a bonus. It meant that she could come to the role fresh, with no baggage. "I wanted to take away all the things that have become second nature to me whenever I see a camera. I've been doing what I do for a long time. Normally it involves being that person – that 'Kylie'. This time I was able to go back to being 11 or 12 again, working on a set and being part of the gang. Blank page, open book."

There's a lot of history to blithely erase. By the time she hit her teens, Minogue was already a mainstay of Australian TV, eventually graduating to the role of feisty, dungaree-clad Charlene in Neighbours, and from there to worldwide pop stardom. She blitzed the airwaves with I Should Be So Lucky and Especially for You, then bounced towards maturity via Better the Devil You Know and the infernally catchy Can't Get You Out of My Head. Her success has been memorialised with a bronze statue on the Melbourne waterfront and a quartet of waxworks at Madame Tussauds. But who knows? It may also come at the expense of an acting career that seemed to get smothered while still in its infancy.

"I'd definitely love to do more acting," she says today. "My heart cries out for it; it's such a deep longing. For years I've been waiting to get back into it and it just hasn't happened. Or, it has happened and it was so disastrous that I thought: 'Oh, it's just not for me.'" Reviewing her role in The Delinquents, for instance, the Mirror sniffed that she had "as much acting charisma as cold porridge", while a co-star slot (opposite Jean-Claude Van Damme) in Street Fighter prompted the Washington Post to dub her "the worst actress in the English-speaking world". Putting aside her playful turn as the Green Fairy in Moulin Rouge!, her screen credits have not been pretty.

On paper, Holy Motors could easily have been another calamity to add to the list. Instead, it winds up as the talk of this year's festival; the most audacious film in competition, for all its wild detours and screeching flights of fancy. So Minogue took a gamble and the gamble paid off. "I've got a lot of work to do before people stop thinking: 'Oh, what's Kylie Minogue doing in a film?'" she admits. "But this has made me feel it's possible to do something beautiful and challenging, and to be believable as someone else."

If Holy Motors is about anything, it's about the roles that we play, the lives we inhabit and the way in which these performances can make one feel that they are living a lie. This must be something Minogue has experienced in her own life. "Oh, absolutely. Totally. For 25 years I've been putting those inverted commas around Kylie." She sips at her water. "It's a weird thing, the world we live in now, where everyone has a cameraphone. There's a line in the film: 'Cameras used to be bigger than us and now we can't even see them.' When I started, there was something almost romantic about the notion of paparazzi. I mean, it wasn't. They were still chasing you down the road. But that guy had to put film in his camera and work out whether it was worth pressing the button to take the shot, otherwise he's got to stop and change the film. So it was like this age of innocence. Whereas now, the cameras are everywhere. So if I'm at home in sweatpants, looking like a total dag, and I step outside?" A shake of the head. "You don't even know where the cameras are any more."

And yet, this being Kylie, she would rather look on the bright side. A moment later she's off again, enthusing about shooting in Paris and being in Cannes; marvelling at the pure, happy accident of finding her way into this oddball, surreal picture that has everyone so excited. "I think I'm having a full out-of-body experience at the moment," she marvels. "When I get back to London, I'll need to see a picture of myself to prove I was here."

Audience complete, the guests again rise up to swamp her. They want her to wait a moment, stand still for a second, while they huddle in and take their photos. Every phone is a camera; there will be proof she was here. "Wow!" exclaims Kylie, posing gamely in the sunshine as the pictures are snapped. "Wow!" The inverted commas are back in place.